Biosensors are used for detecting the presence of a target chemical or biological agent in a wide variety of applications, such as detection of contaminants in air (e.g., in air quality sensors) or detecting the presence of proteins and nucleic acids in blood samples or other samples. A biosensor measures the presence of various chemical components in a sample contained within a biosensor cell. For example, a biosensor may be used to measure the amount of glucose present in a sample of blood.
Some known methods of detection rely on growth cultures. These methods are based on the ability of pathogenic species to multiply in nutrient-rich medium containing selective agents that inhibit the growth of non-target organisms. These detection methods may be used to differentiate between target and non-target organisms. Although sensitive and accurate, these procedures can take as long as several days and thus are not useful for organisms that don't grow easily. Other methods of detection, such as Polymerase Chain Reaction (PCR) and Enzyme-linked Immunosorbant Assay (ELISA), can directly detect pathogen-specific DNA and proteins, respectively, and can be completed in a matter of hours. PCR is extremely sensitive and has been shown to detect as few as 10 or fewer organisms. In comparison, ELISA is less sensitive but has the ability to detect proteinaceous toxins. Together, these techniques can provide highly sensitive and specific detection of pathogens and they are currently the standard techniques used in both the clinics and research laboratories.
Detection of events such as binding of single cells or molecules is generally performed using either optical (usually fluorescent) or electrical detection. Optical techniques are very sensitive and can detect single molecule events but require the attachment of a fluorophore molecule to the target. Optical techniques are more sensitive than are thermal or electrical detection because in optical detection, excitement from a single or few photons, in a process such as electron multiplying or Avalanche phenomena, can be amplified and is sufficient to generate a detectable flow of electrons or charge (current). The ability of a microscope to view simultaneously a large area may be the key. While the fluorescent platforms usually have higher sensitivity and signal to noise ratio (SNR) compared to electrical biosensors, they may not provide real time monitoring possible with electrical biosensors.
Electrical detection method techniques may not require the attachment of fluorophores or other labels but are less sensitive. The devices usually suffer from low signal to noise ratio (SNR) due to different sources of noise (e.g. electrical, thermal, Flicker, Johnson, etc.) and low detection signal (e.g. the signal generated due to a reaction or binding event of a target molecule to the probe molecule is not large enough). As a result, electrical biosensors exhibit lower sensitivity, in comparison to the some optical detection techniques, which can be detrimental to early stage detection and diagnosis.
One or more embodiments may address one or more of the above issues.